The present invention relates to a method and apparatus for controlling the idling speed of an internal combustion engine in accordance with the outputs of sensors for sensing the conditions of the engine.
In the past, with a view to making the idling speed of an engine maintenance free, closed loop (negative feedback) idle control methods have been proposed for always maintaining the idling speed of an engine at a desired speed corresponding to the warm-up condition of the engine.
However, since these prior art methods control the idling speed of an engine so as to always maintain it at a desired value (speed) corresponding to the warm-up condition of the engine irrespective of the will of the driver of the vehicle in which the engine is installed, they still involve many problems. For instance, in the case of the engine of an automobile with a manual transmission, if the foot brakes were applied to the automobile being run during the warm-up to decelerate the automobile and then the clutch was disengaged, since the negative feedback control had been effected and since the idle air flow had been increased due to the actual engine speed being lower than the desired speed, there was the disadvantage of rapidly increasing the engine speed just after the disengagement of the clutch. Moreover, if the clutch was disengaged while the automobile was coasting by the force of inertia, since, due to the negative feedback control and due to the actual engine speed higher than the desired speed, the idle air flow had been decreased extremely so as to decrease the speed, there was the disadvantage of rapidly decreasing the speed upon the disengagement of the clutch and thus causing the engine to stall in the worst case. On the other hand, where the engine cooling water temperature was low with the engine still being at the warm-up operation and the desired engine speed was higher than the actual engine speed, even if the throttle valve was not opened or the accelerator pedal was not yet depressed by the driver, if the transmission was being engaged, due to the operation of increasing the actual engine speed to the desired speed there was the disadvantage of increasing the vehicle speed against the will of the driver or making it impossible to obtain the desired engine braking effect.